An electric vehicle includes a traction battery. The battery has a state of charge (SOC) indicative of the current charging state of the battery. Knowledge of the battery SOC enables usable battery energy and battery power capability to be calculated.
The SOC of a battery may be estimated indirectly. One approach to estimating the battery SOC involves battery current integration (i.e., coulomb counting). A problem with such battery current integration approaches is that highly accurate current sensors are required to ensure the accuracy of the SOC estimation. Another approach uses battery voltage information to estimate the SOC. A problem with such battery voltage translation approaches is that many of them are either map-based or simplified equivalent circuit model based.
A battery is operated around a given battery SOC set-point in charge sustaining driving mode. The battery SOC estimation provided by the noted existing estimation approaches may be valid in this case as the long time duration dynamics are negligible. However, slow diffusion dynamics are dominant in charge depleting driving mode. The battery SOC estimation provided by the noted existing estimation approaches will not be valid due to the high non-linearity of the slow dynamics and dynamic components along wide frequency ranges.
Another battery SOC estimation approach should be developed which can be used over wide SOC, temperature ranges, and various vehicle driving conditions.